1. Field of the Invention
The present invention is generally directed to the field of sealing technology for roller cone drill bits, and, more particularly, to a radial lip seal that may be used on a roller cone drill bit.
2. Description of the Related Art
Oil and gas wells are formed by a rotary drilling process. To that end, a drill bit is mounted on the end of a drill string which may be very long, e.g., several thousand feet. At the surface, a rotary drive mechanism turns the drill string and the attached drill bit at the bottom of the hole. In some cases, a downhole motor may provide the desired rotation to the drill bit. During drilling operations, a drilling fluid (so-called drilling mud) is pumped through the drill string and back up-hole by pumps located on the surface. The purpose of the drilling fluid is to, among other things, remove the earthen cuttings resulting from the drilling process.
When the drill bit wears out or breaks during drilling, it must be brought up out of the hole. This requires a process called “tripping,” wherein a heavy hoist pulls the entire drill string out of the hole in stages of, for example, about ninety feet at a time. After each stage of lifting, one “stand” of pipe is unscrewed and laid aside for reassembly (while the weight of the drill string is temporarily supported by another mechanism). Since the total weight of the drill string may be several tons, and the length of the drill string may be tens of thousands of feet, this is not a trivial job. One trip can require many man-hours and, thus, tripping is a significant expense of the drilling budget. To resume drilling, the entire process must be reversed. Thus, the bit's durability is very important to minimize the number of times a bit is replaced during drilling.
FIG. 1 depicts an exemplary rolling cutter rock drill bit 10 within which the present invention may be used. A “rolling cutter rock drill bit” is also commonly called a rock bit, a rolling cutter drill bit or an oilfield drill bit. The illustrated bit 10 includes a body 12 having three legs 14. In this type of bit, as is known in the art, a cantilevered bearing spindle (not shown in FIG. 1) formed on each leg 14 extends inwardly and downwardly and is capable of carrying a rotatably mounted rolling cutter 18. A plurality of bearings are arranged on the bearing spindle to support the rotatably mounted rolling cutter 18. Attached to each illustrated rolling cutter 18 are hard, wear-resistant cutting inserts 20, which are capable of engaging the earth to effect a drilling action and cause rotation of the rolling cutter 18.
The inserts 20 on the rolling cutters 18 crush and cut the rock as drilling operations are performed with the necessary force being supplied by the “weight-on-bit”(WOB) which presses down on the drill bit 10 and by the torque applied by the rotary drive mechanism. During the drilling process, very large and non-constant stresses and forces may be applied to the inserts 20, the rolling cutters 18, and the drill bit 10 itself. Thus, the loads carried by the internal bearings can be very large and irregularly applied. That is, the rolling cutter 18 bearings are subjected to very irregular loads, with the instantaneous loading on the bearings being several times larger than the average bearing loads.
In such drill bits, some type of seal is positioned between the bearings and the outside environment to keep lubricant around the bearings and to keep contaminants out, e.g., grit or debris resulting from the drilling process. Proper sealing is very important in drilling operations. One type of seal that may be employed in rolling cutter drill bits is a lip seal. Such a seal is positioned in a groove (or gland) formed in the body of the rolling cutter 18. The seal typically has one or more lips that engage the sealing surface of the bearing spindle. One problem with such lip seals is keeping the lip properly oriented and ensuring that all sliding takes place at the interface between the lips of the seal and the sealing surface of the bearing shaft. That is, it is desirable to ensure that substantially all sliding takes place at the lip of the seal and not at some other part of the seal that is not designed for sliding engagement with another part, and to ensure that the lip seal remains properly oriented during drilling operations.
The present invention is directed to devices and methods that may solve, or at least reduce, some or all of the aforementioned problems.